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Enlarge Image Engineering drawing showing the
preliminary design of the Phase 1 RHOV.
(Courtesy WHOI/Lockheed-Martin)
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Enlarge Image Matt James, senior research engineer at Southwest Research Institute, lead contractor on the RHOV project, stands amidst the three ingots of 6Al-4V ELI titanium that will be forged into a new HOV personnel sphere, seen here after fabrication by the Titanium Metals mill in Morgantown, PA. The two larger ingots, each weighing 17,000 lbs, will become the hull hemispheres, and the third ingot (7,000 lbs) will be used to make viewport and hatch inserts.
(Photo courtesy Ben "BK" Miller, SwRI)
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Enlarge Image The titanium ingots are delivered to Southwest Research Institute in San Antonio, TX, prior to being shipped to the forger, Cudahy Forging, a subsidiary of Ladish Co. in Cudahy, WI. (Woods Hole Oceanographic Institution)
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The 13,000-lb titanium billet is heated to 1,700 degrees Fahrenheit and
“edge rolled” to get it as close to circular as possible. After that,
it is paddled to flatten its diameter to 130 inches and to reduce its
thickness to approximately six inches.
(Advanced Imaging & Visualization Laboratory, Woods Hole Oceanographic Institution)
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The titanium disc is placed on a ring die, and the male die is pushed
through the disc to form the first of two hemispheres. Eventually the
hemispheres will be welded together using a high-energy electron beam
to form the submersible’s personnel sphere.
(Advanced Imaging & Visualization Laboratory, Woods Hole Oceanographic Institution)
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Still twice as thick as its will be when completed, the forged
hemisphere cools. Later, material will be removed from both its
interior and exterior to reduce its thickness to three inches and its
overall outside dimension to 7 feet.
(Advanced Imaging & Visualization Laboratory, Woods Hole Oceanographic Institution)
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| The design of a replacement human-occupied vehicle (RHOV) for Alvin is the result of more than 10 years of discussions and input from the scientific community. A 2004 National Research Council (NRC) report, Future Needs of Deep Submergence Science, recommended construction of a new, more capable HOV as part of a suite of tools for ocean research, which includes remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs). The preliminary report of the U.S. Commission on Ocean Policy also points to the importance of research and exploration of the deep seafloor, and to the excitement emanating from such missions to the depths of the ocean.
In 2004, the National Science Foundation approved a WHOI proposal to design the RHOV. Working in consultation with the Alvin user community including the RHOV Oversight Committee and the Deep Submergence Science Committee, WHOI identified goals for the improved capabilities of the new vehicle. Those goals include:
- Increased depth capability (6,500m v. 4,500m)
- Larger personnel sphere
- Improved internal ergonomic design for pilot/observer comfort
- Increased number and size of viewports for expanded observer viewing capability
- Improved speed and maneuverability
- More powerful thrusters provide increased thrust in all directions
- Faster descent/ascent time
- Optimized hydrodynamic shape (faired cross-section)
- Faster variable ballast system pumping rates
- Increased submerged time (8-10 hrs at 2,500m)
- More time on bottom for science
- Eliminate the mercury trim system
- Employ an environmentally safe system that uses moveable tungsten weights to control RHOV pitch & trim
- Eliminate use of drop weights for shallower dives
Technical Challenges
The RHOV will present a number of technical challenges. New
flotation material capable of withstanding greater pressures must be fabricated
and certified for use. Forging and welding the three-inch-thick titanium
personnel sphere is complex. New types of batteries to power the vehicle will
be required, and a variable ballast system must be designed to adjust for
changes in payload, to enable the sub to descend and ascend, and to hover to
conduct research in the mid-water zone.
The RHOV will require no major modifications to the 274-foot
Research Vessel Atlantis, its support
ship, and its operating costs will be similar to those of Alvin.
A New Personnel Sphere
To achieve the goal
of a deeper-diving sub with better ergonomics and field of view, a new
personnel sphere, capable of withstanding pressure at 6,500 meters, will need
to be forged. At maximum depth, there will be roughly 10,000 pounds of pressure
on every square inch of the sphere’s exterior, though for the pilot and
two science observers the inside air volume remains at normal
atmospheric pressure.
Like the existing Alvin personnel sphere, the new sphere
will be made of titanium, a very strong and relatively lightweight
material. Two titanium ingots, each
weighing 17,000 pounds, have been forged into two hemispheres in a process that
requires multiple heat and pressure cycles. An additional 7,000-lb ingot will be used to make viewport and hatch inserts. The two hemispheres will be
further heat treated and welded together to make a single three-inch-thick
sphere.
Phased Approach
Phase 1
In August 2008,
following months of analysis and discussion between WHOI and NSF, we have
proposed to NSF that we take a phased approach to building the 6,500-meter
RHOV.
In
Phase 1, we will achieve most of the goals of the originally proposed RHOV,
while maintaining the option of upgrading to a 6,500-meter depth capability at a
later date. The enhancements to the existing submersible during the first phase
include:
- Larger personnel
sphere with improved interior electronics, ergonomics and overlapping field of
view for pilots and observers;
- Increased battery
capacity, giving researchers more on-bottom time;
- Increased sampling
basket load limits and improved manipulator performance;
- Better
maneuverability and improved mid-water research capability;
- Improved lighting and video systems
WHOI
is preparing a detailed plan for the phased approach, which includes
development of a robust design and project management plan to achieve the
near-term increased capability and the longer-term goal of a 6,500m RHOV.
The
timeline includes a preliminary design review and cost analysis in June 2009,
with a final design and cost review in the fall of 2009. When the project successfully passes these
reviews, we will have a design-based estimate of the construction costs. With this plan in place, we expect to pursue
the additional funds needed to bring the Phase 1 RHOV into service.
Phase 2
Every three to four
years the HOV undergoes a complete maintenance overhaul. When the Phase 1
vehicle is ready for its first overhaul, a decision can be made about
completing the enhancements: increasing
the operating depth to 6,500 meters, replacing the drop weights for ascent and
descent and replacing the mercury trim system.
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Alvin |
RHOV - Phase 1 |
RHOV - Phase 2 |
Depth
|
4,500 m
|
4,500 m
|
6,500 m
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| Sphere Volume |
144.2 cu ft |
170.8 cu ft |
170.8 cu ft |
| External Science Payload |
275 lbs |
>275 lbs |
400 lbs |
| Internal Science Payload |
6,630 cu in of 19" rack space |
12,300 cu in of 19" rack space |
12,300 cu in of 19" rack space |
| Max Speed (fwd) |
2 kts |
2+ kts |
3 kts |
| Max speed (lateral) |
Minimal lateral ability |
0.5 kts |
0.5 kts |
| Max Speed (vertical) |
30 m/min |
30 m/min |
48 m/min |
| Trim Angle |
+/- 7.5 deg |
+/- 7.5 deg |
+/- 15 deg |
| Positioning control |
Manual w/ auto heading |
Auto heading, DP, track and following control |
Auto heading, DP, track and following control |
Last updated: November 9, 2009 |
